Electrical devices such as electrical motors may comprise an electrically conducting rotatable device, for example a commutator or slip ring, which connects to rotor windings of a rotor arranged inside a stator. Commutators for example, are in mechanical contact with brushes while rotating, enabling current to flow through the commutator to the rotor windings. The brushes are typically made of carbon, sometimes with copper particles dispersed in the carbon to increase conductivity. Due to mechanical friction the brushes are eventually worn down, and electrically conducting particles coming loose from the brushes due to wear may spread inside the stator, increasing the risk of short circuiting the electrical device. It would hence from at least two aspects be desirable to decrease the mechanical wear of brushes.
WO2004/088695 discloses a device for making or breaking electric contact between two electrodes for example in an electrical motor, to replace the commutator brush. The device comprises magnetic nanostructures dispersed in a dielectric liquid between the two electrodes, and a controllable magnetic field means to control the movement of the magnetic nanostructures. The magnetic nanostructures may thus be aligned depending on the magnetic field, in order to provide current flow between the two electrodes.
Magnetic nanostructures are however not ideal electrical conductors. Although WO2004/088695 discloses that the magnetic nanostructures may comprise an electrically conducting coating, a coating process of nanostructures may be difficult to control to obtain optimal coating thickness. There is furthermore a contact resistance between each pair of nanoparticles which due to the relative hardness of the magnetic nanoparticles and the large number of contact resistances due to the small size of the nanoparticles, leads to significant losses.